Telephone system



Jan. 11, 1944.

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//v VEN TOR J. BAUMFALK ATTORNEY Jan. 11, 1944. J. BAUMFALK Filed April 2, 1942 vqN L Udmw wwwb Kw 2w h I l L h- Ill l :T im n 2615 EN WNW .b JU a b a w W EIUFI MN I @3333 1 L -l m N NMU v ATTORNEY i .Jan. 11, 1944. J. BAU MFALK TELEPHONE SYSTEM Filed April 2, 1942 10 Sheets-Sheet 3 QWNEEE TJUPI Jan. 11, 1944. J. BAUMFALK TELEPHONE" SYSTEM 10 Sheets-Sheet 4 Filed April 2, 1942 a v i Lg] lNl/EN TOR J. BAUMFAL K A r ram/5k Jan. 11, 1944. J. BAUMFALK 2,338,752,.

TELEPHONE SYSTEM Filed April 2, 1942 10 Sheets-Sheet e ATTORNEY Jan. 11, 1944. IBAVUMFALK TELEPHONE SYSTEM Filed April 2, 1942 10 Sheets-Sheet 7 art lNVENTOR By BAUMMLK @QCZML ATTORNEY Jan. '11, 1944.

J. BAUMFALK TELEPHONE SYSTEM Filed April 2, 1942 1O Sheets-Sheet 8 ,wvs/vroe By JBAUM-XLK Arm/away Jan. 11, 1944. 'J. BAUMFALK 2,338,752

' TELEPHONE SYSTEM Filed April 2, 1942 10 Sheets-Sheet 9 lNl/EN 70/? By J. BAUMFALK A TTORNE V Jan. 11,1944. 1. BAUMFALK 2,338,752

TELEPHONE SYSTEM Filed Apri1 2, 1942 10 sheets-sheet 10 MARG/IYAL Ml VE/V 70/? V J. BAUMFMLK A TTORNEY Patented Jan. 11, 1944 UNITED STATES PATENT OFFICE Telephone Laboratories, Incorporated,

New

York, N. Y., a corporation of New York Application April 2, 1942, Serial No. 437,397

Claims.

This invention relates to telephone systems and particularly to systems comprising impulse controlled selector switches for establishing connections between calling and called lines.

Objects of the invention are an increase in the efliciency of the switching apparatus and trunking arrangements of semiautomatic telephone systems and particularly an increase in the capability and efficiency of trunk circuits and selector switches used in establishing intertoll connections.

This invention is an improved trunking and switching arrangement in a toll office whereby calls incoming over intertoll trunks are routed through an intermediate dialing trunk circuit and an associated incoming trunk circuit to an intermediate toll operators position, each call being answered by insertion of the answering plug of a cord in the answering jack associated with the incoming trunk circuit to which the call in question is routed. Some incoming calls are further extended manually by inserting the calling plug of the cord in the outgoing jack of an intertoll trunk or trunk to a local ofiice. Other incoming calls are further extended under control of the intermediate toll operators dial, the calling plug being inserted in a dial jack which is associated with the intermediate dialing trunk circuit through which the incoming call is routed to the intermediate toll operator. The dialing of the desired toll or local route effects the selective operation of a selector which is associated with the intermediate dialing trunk circuit, the selector having access to groups of intertoll trunks and to groups of trunks to local oilices as required.

According to one feature of the invention, the intermediate toll operator may receive supervisory signals incoming from the calling toll oflice as long as the answering plug of the cord is connected to the incoming trunk circuit and may receive supervisory signals incoming from the called toll or local office as long as the calling plug is connected to the dial jack. According to this feature disconnection of the cord from both the answering and dialing jacks is effective to lock the intermediate toll operator out of the connection, supervisory signals being transmitted in both directions through the intermediate dialing trunk circuit between the calling toll office and the called toll or local office.

According to another feature of the invention rering signals from a calling toll operator are transmitted through the intermediate dialing trunk circuit to the called toll office on calls wherein the associated selector has selected an intertoll trunk in a group carrying through traffic; but on calls wherein the selector has selected a trunk to a local office or an intertoll trunk in a group carrying terminating trafiic, a rering signal from the calling toll operator eifects the release of the selector and effects the signaling of the intermediate toll operator.

A further feature of the invention is the prevention of interference with a call which is further extended by an intermediate toll operator by connecting the calling plug of a cord to the outgoing jack of an intertoll trunk or trunk to a local office, in case the plug of another cord is inserted in the dial jack of the intermediate dialing trunk circuit through which the call is routed to the intermediate operator. According to this feature, operation of'the ringing key associated with the answering plug of the intermediate operators cord enables the transmission of supervisory signals from the incoming trunk circuit to the distant calling operator and renders the insertion of a plug in the dial jack ineffective to interfere with the manually completed con nection,

A clear and complete understanding of the invention will be facilitated by considering a system in which the various features of the invention are embodied, one such system being shown in the drawings which form a part of this specification. The invention is, however, not limited in its application to the particular system shown but is generally applicable to intertoll switching systems comprising impulse controlled switches.

Referring to the drawings:

Fig. 1 shows, in a first toll office, an operators position comprising a cord CDI, telephone and dial, a jack Jl terminating an outgoing trunk circuit OT! and a signaling circuit CS! connecting the outgoing trunk circuit QTi with a toll line or intertoll trunk TLI;

Fig. 2 shows, in a second toll office, a signal circuit CS2, an associated outgoing trunk circuit 0T2 terminating in a jack J 2, a two-way trunk circuit 'I'WT2 and a toll selector TSZ, all associated with the toll line 'ILl;

Fig. 3 shows an intermediate dialing trunk circuit IDT including a dial jack DJ at an intermediate toll operators position;

Fig. t shows an incoming trunk circuit IT, associated with the intermediate dialing trunk circuit IDT of Fig. 3, terminating in a jack J4 at an intermediate toll operators position comprising a cord CD4, telephone and dial;

Fig. 5 shows a combined intertoll and toll transmission selector CS associated with the intermediate dialing trunk circuit IDT of Fig. 3;

Fig. 6 shows a toll connector switch TC in a local step-by-step dial ofice which is connected to a set of terminals in the bank of the selector CS of Fig. and further shows a two-way trunk circuit TWTE, outgoing trunk circuit OTE, and signaling circuit CSfi associated with anintertoll trunk TL-fi, :the two-way trunk circuit ,TWTS being connected to a set of terminals in the bank of the selector CS;

Fig. 7 shows an auxiliary toll route selector TSl which may be associated with the intermediate dialing trunk circuit I-DTof Fig. 3 in place of the selector CS of Fig. 5;

Figs. 8 and 9 show a trunk circuit CDT! associated with a trunk CDT leading to .a community dial ofiice, this trunk circuit being connected to a set of terminals in the bank of the selector TS] of Fig. 7;

'Fig. lfl'shows a trunkcircuit CDT2 associated with the trunk CDT in the community dialofiice, shows alinc finder LF! and first selector SI for connecting a'calling line to the trunk CDT, and shows a trunk finder incoming selector IS and connector Cl for use in completing calls incoming over the trunk CDT from the toll 'ofice;

Fig. 11 shows the relative positions in which Figs. 1 to fiare to be placed to form an operative arrangement; and V Fig. 12 shows the relative positions in which Figs. 1, 2 '3, 4, 7, 8, 9 and -are to be placed to form anoperative arrangement.

The system represented in the drawings includes a plurality of toll offices each of which comprises a toll board with operators positions and cords for answering calls incoming from local manual or dial ofiices. from toll subscribers lines, from community dial ofiices or from other toll offices; and for connecting calling intertoll trunks with switching trunks leading to called, manual or dial local ofiices, to call toll subscribers lines, to trunks to community dial oifices or to intertoll trunks to other toll offices. Outgoing jacks are connected 'toswitching trunks, toll lines, trunks to community dial ofiices and intertoll trunks. Answering jacks are connected to recordingtrunks,'toll'subscribers lines, trunks from community dial oilices and Intertoll first selectors are provided for use on calls incoming over intertoll trunks to establish connections with other toll, local or community dial ofiices and to route calls .to an intermediate, dialing operators position. The .toll operators positions are provided with dials for .usein controlling the operation of intertoll selectors in the sameand other toll offices and for controlling the operation of selector and connector switches in local or community dial offices. Whilenot shown in the drawings, the operators positions may be provided with key-sets in place of dials, in which case senders are associated with the outgoing trunks 'to register the key-set impulses and controlcthe selectors.

Reference may be had .to the patents to R. 'E. King et al. No. 2,208,765 granted July 23, 1940, and No. 2,209,777 granted July .30, 194.0, for a detailed disclosure of cord and operators position circuits provided in each of the two toll offices for interconnecting calling and called lines and trunks .andfor controlling the completion of toll calls. The outgoing trunk circuits OT! and GT2, two-way trunk circuit TWT2, and intertoll first selector TSZare all similar to corresponding cirintertoll trunks.

cuits disclosed in the aforementioned King et al. patents.

The intermediate dialing trunk circuit IDT is connected to a set of terminals in the bank of intertoll selectors such as TS2 and is associated with an incoming trunk circuit, such as IT shown in Fig. 4 and with a selector circuit which may be a combined intertoll and toll transmission selector circuit, such as theselector CS shown in Fig. 5; or the selector associated with trunk circuit IDT may be an auxiliary toll selector, such as the selector TS! shown in Fig. 7. The incoming trunk circuit IT is similar to the incoming trunk circuit shown in the aforementioned King et al. Patent 2,208,765. The combined intertoll and toll transmission selector circuit CS is similar to the selector circuit CS shown in the copending application of P. W. Wadsworth filed March 20, 19%1, Serial No. 384,238. The toll connector circuit TC is similar to the toll connector TC disclosed in the patent ,toE. .D. Butz, No. 2,021,286 grantedjNovemberlQ, .1935. Although not shown in the drawings, one or more intermediateselectors may be provided in :the step-by-step office for establishing connections with called lines. The selector TS? is similar to the selector T84 shown in the copending application of J. G. Walsh, Ser. No. 437,398, filed April 2, 1942. The community dial trunk circuits CDT! and CDTZ shown in Figs. 8, 9 and 10 are similar to corresponding circuits disclosed in the King et al. Patent No. 2,209,777.

Assume now that an operator in the toll onice comprising the outgoing trunk circuit OTI answers a call with the plug AP! or cord CD1 and then inserts the calling plugCPl in jack J I of the outgoing trunk circuit OTI. A circuit is thereupon closed for operating relay 1%; and relay Hld effects the operation of relay lit and closes a circuit for operatively energizing the upper winding of signaling relay Hill, as described in the first-mentioned King et al. patent. When relay l lfl operates, signaling battery is connected through the front contact of relay Mil, through conductor Wiretard coil ltd, middle winding of composite signaling relay Hit, upper winding of retard coil 5-55, upper conductor of toll line TLl, upper winding of retard coil 2% of signaling cirsuit-CS2 in the second toll o-ffice, to the windings of composite signaling relay 270. Relay 2'50 opcrates, closing a circuit from ground through its front contact, conductor 263, back contact of relay 2! Q of outgoing trunk circuit 0T2, back contact of relay 27d of two-way trunk circuit TWTE, back contact of relay 217, through the winding of relay 27.3 to battery. Relay 2T3 operates, connecting ground toconductor 253 to guard the toll line TLI from seizure in the second toll ofilce. Re1ay 2l'3 closes a circuit for operating relay 275, this circuit being traced from ground through the front contact of signaling relay 2713, conductor 263, back contact of relay 2m, back contact of relay 2M, winding of relay 275, a front contact of relay 273 thence in simplex through both windings of retard coil 2553, conductors 261 and 262, back contacts of relay 238, conductors 2H and 272, inner front contacts of relay 213, conductors 28! and 282, back contacts of relay 2%, through resistors 235, 235 and 281 and through the winding of relay 2% to battery. The line relay 288 of toll selector TS? is thereby operated in series with relay 2'55 of two-way trunk circuit TWTZ. Relay 275 closes a circuit through resistor 2'36 for holding relay 273, and closes a circuit for operating the slow-to-release relay 211. Relay 211 also closes a holding circuit for relay 213 and connects ground potential to conductor 283 to hold the selector T82 and any succeeding switches or trunks through which a connection may be established. When the calling operator operates the dialing key, not shown, the upper winding of relay I40 is controlled by the impulse contact of the dial. Each release and reoperation of relay I40, in response to the dialing of the first digit of the called number, opens and closes the circuit through conductor I64 and toll line TLI, causing a corresponding release and reoperation of relay 210 of signaling circuit CS2. Relay 219 repeats these dial impulses to relay 215 of two-way trunk circuit TWT2 and to relay 288 of selector TS2. Each release of relay 215 opens the operating circuit of relay 211; but, since relay 211 is low in releasing, it maintains the connection of ground to conductor 283 during the response of relays 215 and 288 to dial impulses. The alternate release and reoperation of relay 288 causes the brushes of selector TS2 to be stepped up to the level corresponding to the digit dialed. At the end of the train of impulses, the brushes 29L 292, 293 and 294 are advanced step by step in the selected level to hunt for and seize a set of terminals connected to an idle trunk. When an unguarded set of terminals is found relay 290 is operated to disconnect relay 288 and connect toll line TLi through brushes 29| and 292 and the engaged terminals to the next line, trunk or selector through which the desired connection is being established. For a detailed description of the operation of selector TSZ, reference may be had to the aforementioned King et al. patents.

Assume now that the first digit dialed by the calling operator operates the selector TSZ to select the level represented by terminals 295, which terminals are connected to the intermediate dialing trunk circuit IDT of Fig. 3. Upon selection of the terminals 295 and operation of relay 298 of selector T52, a circuit is closed from ground through the front contact of relay 210, conductor 263, back contact of relay 2! 9, back contact of relay 214, winding of relay 215, a front contact of relay 213, both windings of retard coil 26%, con-- ductors 26! and 262, back contacts of relay 23c, conductors 21! and 212, front contacts of relay 213, conductors 281 and 282, front contacts of relay 290, brushes 23| and 292, conductors 3M and 302, back contacts of relay 31%), conductors 40! and 402, both windings of retard coil 406, thence through resistors 481, 468 and 409 and the winding of relay 4|0 to battery. Relay 419 closes a circuit, which includes the inner lower back contact of relay 428, for lighting the answering lamp AL4 associated with jack J4 at an intermediate dialing operators position. Relay 41!! also connects the ringing current source 4! l through the uppermost front contact of relay 4H], the inner upper back contact of relay 429, condenser 428, conductor 422, condenser 4B8, conductor 492, and a back contact of relay 310 to conductor 3%, to transmit an audible ringing signal to the calling operator to indicate that an intermediate toll operator is being signaled. When the plug A1 4 of a cord CD4 is inserted in jack J4 to answer the call, battery is connected to the sleeve conductor of jack J4, thence through conductor 423 to operate relay 424. Relay 424 closes a circuit for operating relay 425. Relay 425 opens the bridge comprising condenser 42B and resistor 421 normally bridged across conductors HI and 422 and closes a circuit for operating relay 428, this circuit being traced from the winding of relay 428 through the inner lower front contact of relay 425, inner lower front contact of relay are, conductor 493, uppermost back contact of relay 310, conductor 3B3, brush 293 of switch TSZ, a front contact of relay 298, through conductor 283 to.

round at a front contact of relay 211. Relay 428 looks to the same ground under the joint control of relays 425 and 483 but independent of relay 4H], opens the audible ringing tone connection, extinguishes the answering lamp AL4, and closes a circuit for operating the answering supervisory relay 356 of trunk circuit IDT. This circuit is traced from ground at the uppermost front contact of relay 425, through the back contact of relay 4H3, uppermost front contact of relay 423, conductor 404, lower back contact of relay 330, through the upper Winding of relay 356 to battery.

When the dial key at the calling operators position in the first toll ofiice is restored to normal, relay 139 of outgoing trunk circuit OT! is operated and relay hill is held under control of relay let in the manner described in the firstmentioned King et al. patent. The talking circuit between the calling operator in the first toll office and the answering operator in the second toll ofiice includes conductors it: and H52, front contacts of relay E32 conductors l5! and E52, repeating coil RCl, condensers $5, the conductors of toll line TLI, condensers 2'65, repeating coil RC2, conductors Zti and 232, back contacts of relay 230, conductors 2H and 212, front contacts of relay 213, conductors 28! and 2&2, front contacts of relay 2%, brushes 29] and 292, conductors 3M and 392, back contacts of relay 3W, conductors 40! and 4532, condensers 4i"! and .13 and conductors 422i and 422.

Calls to be completed manually If the call is one that is to be completed through an outgoing trunk jack in the trunk multiple at the answering intermediate operators position, the operator inserts the calling plug 0P4 in the outgoing trunk jack, such as J5, and operates the ringing key RK to actuate its upper contact springs, thereby to operate ringing relay die of the trunk circuit IT as described in the first-mentioned King et 'al. patent. The operation of relay H9 connects ground at the uppermost front contact of relay 4225, through the front contact of relay 4H conductor 4335, inner upper back contact of relay of trunk circuit IDT to the upper winding of relay 2336, thereby operatively energizing relay 333. The operation of relay did also disconnects ground from conductor #lil i, thereby causing the release of relay 355. As soon as the ringing relay 4E9 releases, due to the release of the ringing key of the cord circuit ground is connected through the outer upper front conta t of relay 425, back contact of relay Mil, upper front contact of relay 428, conductor 3M, a back contact of relay 355, through the inner lower front contact of relay 339 to the lower winding of relay 33 thereby locking relay 35B operated; and the grounded conductor sea is further connected through the upper front contact of relay 336, conductor 3&4, brush 2% of selector T82, a front contact of relay 2%, conductor 28:1, to the winding of relay Eli oi twoway trunk circuit TWTZ, thereby causing the operation of relays 235. Relay 21%) connects signaling battery through its front contact, back contacts of relays 218 and 24B, conductor 254,

retar'd coil 25%, middle winding of relay 27d, and upper winding of retard coil 256 to the upper conductor of toll line TL! to operate signaling relay lid of signaling circuit CS! in the calling tol1 ofiice. The operation of relay l'lil causes the operation of relay thereby opening the circuit path through the lower, low-resistance winding of relay N54 to extinguish the supervisory lamp associated with plug CH of cord CDI.

Supervisory signals, received by relay MS from the called toll or local oflioe are repeated by relay 219 to the calling toll operator. A rering signal from the calling operator eifects the release and reoperation of relays Hid, 2'58, 2'55 and Mil. The release of relay lit closes a circuit for operating relay H3, this circuit being traced through a back contact of relay are, conductor Gilt, back contact of relay 3H3, conductor 303, brush 293, front contact of relay 2%, conductor 283, to ground at a front contact of relay 21! of two-way trunk circuit TWT2. Being slow in releasing, relay 2?? remains operated, when relay Mi releases, in response to a rering signal. Relay lls connects the winding of relay 4M in parallel with the winding of relay ll-i. Relay 424 operates and locks independent of relay MS. When relay lii! reoperates at the end of the ringing signal, relay M3 releases, and relay H5 is alternately operated and released under the control of interiiupter Mil. Each time relay H5 operates it closes a circuit for holding relay M l and disconnects the winding of relay did from conductor 42S thereby reducing the current through this conductor to extinguish the supervisory lamp associated w th the answering plug AP l. When the intermediate toll operator operates the talking key (not shown) of cord CD4, relay M4 releases but relay 424 is held operated in the manner described in the aforementioned King et al. patents.

When the calling operator releases the connection by removing plug CPl from jack J l relays lil i, H6, 5553 and 1% are released. The release of relay its causes the release of relay 219. The release of relay 2193 causes the release of relays 2'i5 and 2H in succession in two-Way trunk circuit TWTZ and the release of relay MD of incoming trunk circuit IT. The release of relay 2T? disconnects ground from conductor 283 thereby causing the release of relay 2% of selector T52 thereby causing this selector to be restored to normal. The release of relay MB of trunk circuit .IT closes a circuit for operating relay M3. The operation of relay M3 connects the winding of relay l! in parallel with the winding of relay 425 thereby reducing the resistance in the circuit through conductor 623 to light the supervisory lamp associated with the plug AP l of cord CD5 as a disconnect signal to the intermediate toll operator. Since relay H0 does not reoperate, relay 4H3 releases when ground is disconnected from conductor 333 due to the release of relay 27'! of two-way trunk circuit TWTZ. Relay (H 2 operates and looks; but both of relays 42:3 and M4 release when the intermediate toll operator removes the plug AP l from jack J l. The release of relay 424 causes the successive release of relays are and 28. The release of relay 425 also causes the release of relay of trunk circuit IDT.

Calls completed through selector CS To complete a desired connection under control of the answering intermediate toll operators dial, the answering operator inserts the calling plug CP4 in the dial jack DJ of the intermediate dialing trunk circuit IDT thereby causing the operative energization of the upper Wind ing of relay 3%. Relay $54 closes a circuit including a front contact of relay 356 for operating relay 555. Relay 355 closes a circuit through the lower, low-resistance winding of relay 354 to light the supervisory lamp associated with plug CH, and closes a locking circuit for relay 356. When the answering intermediate toll operator actuates the dial key, not shown, relay 456 is operated and battery is connected through the impulse contacts of the dial, to the ring conductor of plug CP l as described in the aforementioned King et al. patents to operate relay 351; and battery is connected through to the tip conductor of plug GP to operate relay 3%. Relay 353 closes a circuit, including the inner lower front contact of relay 358 and a front contact of relay for operating relay 359; and relay 3% locks under the sole control of relay 355. With the dial key operated and conductor 3% connected to ground through the low resistance winding of relay 354, a dial pilot lamp is lighted at the operators position as a start dial signal in the manner described in the aforementioned King et al. patents The operation of relays 35! and 359 closes a circuit for operating the line relay 51.! of the associated selector circuit CS shown in Fig. 5, this circuit being traced from ground at the inner lower front contact of relay 359, through the lower back contact of relay 36?, front contact of relay 357, upper contact of test jack TJl, back contact of relay 34 i, middle lower back contact of relay 35S, thence in simplex through resistors 36! and 362, lower front contacts of relay 359, windings of retard coil 3%, conductors 39! and 392, back contacts of relay of selector CS, back contacts of relay 5E2, through resistors SH and 5M, thence through resistor Elli, uppermost back contact of relay set in parallel with the lowermost back contact of relay 5%, through the winding of relay 522 to battery at the back contact of release magnet 52$. Relay 52! closes a circuit for operating relay 522. Relay 522 connects ground through its inner front contact and a back contact of relay Elli) to the winding of a permanent signal alarm relay 557 which is common to a ground of selectors and operates to cause a maintenance alarm in usual manner in case no dial impulses are received by a seized selector within a predetermined interval of time.

When the intermediate toll operator dials the first digit of the called toll route number, relay 535i is alternately released and reoperated to repeat the dial impulses to relay 52!. The release of relay 521 in response to the first dial. impulse closes a circuit from ground at the inner upper sack contact of relay 5H9, through the back contact of relay 52 I, upper front contact of relay 522, right contact of test key TK, back contact of relay 539, winding of relay 523, and through the winding of the vertical stepping magnet to battery. The stepping magnet 52? is thereby operated to step the brushes up to the first level of the terminal bank. Vertical off-normal springs 5&0 are actuated when the brush shaft moves out of normal position. Relay 523 is operated in series with magnet 52?; and, when springs 540 are actuated, a circuit is closed from battery at the back contact of release magnet operating release magnet 529.

523, through the upper contact of springs 540, winding of relay 525, front contact of relay 523, conductor 9, to ground at a front contact of relay 522. Relay 525 locks under control of rotary stepping magnet 528, independent of relay 523; this locking circuit is traced from battery at the back contact of release magnet 529, through the upper contact of springs 540, winding of relay 525, back contact of rotary-stepping magnet 528, to ground at the lower front contact of relay 525. Relay 523 closes a circuit for operating relay 501; and relay 50'! looks under control of relays 530 and 522, but independent of relay 523. When relay 52! operates at the end of the first dial impulse, magnet 52'! releases; but relay 523 is slow in releasing and remains operated until after relay 52! has reoperated at the end of the last impulse in the train. Relay 522 is slow in releasing and remains operated during the response of relay 52! to dial impulses. The release and reoperation of relay 52! in response to each succeeding impulse in the train created by the dialing of the first digit by the answering operator, causes a corresponding operation and release of the vertical stepping magnet 52'! thereby advancing the brushes to the level corresponding to the digit dialed. When relay 523 releases at the end of the train of impulses, it opens the operating circuit of relay 525 but relay 525 is held operated under control of springs 549 and stepping magnet 528.

Assume now that the first digit dialed by the intermediate operator is one which is to be absorbed, the stepping of the brushes to the corresponding level being efiective to actuate normal post springs 54! without actuating springs 542.

The actuation of springs 54! closes a circuit for operating relay 545, this circuit including back contacts of relays 544 and 543, front contact of springs 54!, lower back contact of relay 505, upper front contact of relay 52! and a back contact of relay 5M. The operation of relay 545 prevents the operation of the rotary stepping magnet 528 when relay 523 releases, and connects battery to the windings of relays 52! and 522 independent of release magnet 529. When relay 523 releases at the end of the train of impulses, a circuit is closed for operating relay 544; this circuit includes front contacts of relays 545 and 525, the back contact of relay 523, conductor 5!!! and a front contact of relay 522. Relay 544 locks, under control of relays '5l2 and 522, and closes a looking circuit for relay 545 which is traced through the lower front contact of relay 544, inner lower front contact of relay 545, upper front contact 1 of relay 52!, to ground at a back contact of relay 55D. The aforementioned release of relay 523, at the end of the first digit, closes a circuit for This circuit is traced from battery through the outer lower front contact of relay 545, middle contact, of springs 545, winding of release magnet 529, front contacts of relays 545 and 525, back contact of relay 523, conductor 5H3, to ground at a front contact of relay 522. The operation of release magnet allows the brush shaft to be restored to normal in usual manner. When the shaft reaches normal position, the return of springs 549 to normal causes the release of magnet 529 and the release of relay 525. When the intermediate operator dials the next digit, the dial impulses are again repeated by relay 35? to relay 52!. The

-release and reoperation of relay 52! in response [to each impulse of the train causes a corresponding operation and release of the vertical stepplng magnet 52'! to step the brushes to the desired level. The release of relay 52! in response to the first impulse also causes the release of relay 545. Relay 523 operates in series with magnet 52'! and remains operated until all of the impulses in the train have been received. When the shaft moves out of normal position, the actuation of springs 54K! closes the circuit for operating relay 525; and relay 525 locks under control of rotary stepping magnet 528. Since relay 544 is locked operated, relay 545 is not again operated in case the level selected in response to the second. train of impulses is one on which normal post springs 5 are actuated. When relay 523 releases at the end of the second train of impulses, or when relay 523 releases at the end of a first train of impulses and relay 545 is not operated, a circuit i closed for operating rotary stepping magnet 528 to step the brushes into engagement with the first set of terminals in the selected level. The circuit for operating magnet 528 includes the upper back contact of relay 545 upper front contact of relay 525, back contact of relay 523, conductor m and a front contact of relay 522. The operation of stepping magnet 528 causes the release of stepping relay 525 and the release of relay 525 causes the release of stepping magnet 528. The release of stepping magnet 528 closes a testing circuit from battery at the back contact of release magnet 529, through the upper contacts of spring 549, Winding or relay 525, back contact of stepping magnet 528, inner lower back contact of relay 538, through test brush 533 to the engaged test terminal. If the line, trunk or selector connected to the engaged set of terminals is busy, the test terminal has ground potential connected thereto as a guarding potential; and stepping relay 525 reoperates, closing the circuit for operating rotary stepping magnet 528. The stepping magnet 528 then steps the brushes into engagement with the next set of terminals and causes the release of relay 525; and the release of relay 525 again causes the release of stepping magnet Relay 525 and stepping magnet 528 thus cooperate to advance the brushes step by step in the selected level to hunt for an unguarded set of terminals. When the test brush 533 engages a terminal which is not comiected to ground, the release of magnet 528 closes a circuit for operating relay 539 this circuit is traced from battery at the back contact of release magnet 529, through the upper contact of springs 549, winding of relay 525, back contact of stepping magnet 528, winding of relay 535, conductor 5 9 to ground at a front contact of relay 522. Being marginal, relay 525 does not operate in series with relay 530. Relay 539 connects ground at the outer lower front contact of relay 522, through conductor 559, inner lower front contact of relay 535, and brush 533 to the engaged terminal as a busy guarding potential; and opens the circuit for operating alarm relay 541.

Assume now that the level in which trunkhunting occurs is one in which the terminals are connected to trunks leading to a local dial ofiice, such a level being represented by the terminals 531. In such a case the normal post springs 542 are not actuated, relays 555 and 5 9 are not operated, and the operation of relay 530 is ineffective to disconnect relay 52I from conductors 5i]! and 582. As shown in the drawings, the terminals 53! connect directly to a toll connector TC in a local step-.by-step ofiice, but intermediate selectors may be provided if necessary to give access to all subscribers in the local dial oflice in which case -the terminals 53'? would be connected to an intermediate selector. The ground potential connected through brush to conductor 553 is further connected through a back contact of relay 3% of connector TC, conductor 554, brush 534, a back contact of relay 535, outer lower front contact of relay 533 and through the upper front contact of relay 537 to the winding of relay 537 to hold this relay operated under control of relay 533 of the toll connector. Relay 533 disconnects the winding of relay 52.3 from the back conof relay 533, brush 53!, conductor 55!, a back contact of relay 335, and through the right winding of relay 33! to ground. Relay 65! closes a circuit for operating relay 332; and relay 682 looks through its inner upper front contact and a back contact of relay 633, through conductor 553, brush 533, inner lower front contact of relay 530, to ground at a front contact of relay 522. The trains of impulses created by the dialing of the last two digits of the called local subscribers number are repeated by relay 35! to relay 52l; and relay 525 repeats these impulses to relay 55! to effect the selective operation of the toll connector TC to seize the called subscribers line. For a complete description of the operation of a toll connector reference may be had to the aforementioned patent to D. Butz. When the brushes of toll connector TC engage the terminals of the called line and the called line is idle, relay 6% is operated by the energization of its lower winding in series with test brush 693 and the winding of cut-off relay 393 of the called subscribers line circuit. Relay 635 looks to conductor 553, disconnects relay 50! from conductors 55! and 552 and opens the connection between conductors 553 and 554, thereby causing the release of relays 531, 632 and 551. The release of relay 53! opens the bridge through resistor 536 across brushes 53d and 533, connects the lower winding of relay to brush 53! and closes a circuit for operating relay 5l2. Relay 5l'2 opens the normally closed short-circuit across the left windings of repeating coil RC5, connects talking condenser 5H between these windings, and connects the upper winding of relay 520 to brush 532. The release of relay 352 closes the ringing circuit for signaling the called station. If and when the call is answered, relay 602 is reoperated and looks through conductor 554, brush 534, a back contact of relay 535, a front contact of relay 533, a back contact of relay 53?, conductor 5l9 to ground at a front contact of relay 522. With relays 39B and 632 operated, the called line L is connected through brushes Gel and 632, front contacts of relays i532 and 333, conductors 55! and 552, brushes 535 and 532, front contacts of relay 538, back contacts of relay 510, right windings of repeating co-il RC5, a front contact of relay 5 l 2, and a back contact of relay 531, through the windings of relay 523 to talking battery. The operation of relay 523 connects ground to conductor 394, operating supervisory relay 315 of trunk circuit ID'I. Relay 335 opens the circuit through the low-resistance, lower winding of relay 354, to

extinguish the supervisory lamp associated with the plug CF4 of cord- CD4.

When the intermediate toll operator restores her dial key to normal, battery is disconnected from both the tip andthe ring conductors of the calling plug CP i thereby releasing relays 351 and 358 in the manner described in the aforemen tioned King et al patent. Relay 353i releases first and connects ground to conductor. 33% to maintain the simplex circuit beginning atresistors 36| and 362, to hold relay 52| of selector CS. Relay 358 opens the operating circuit of relay 355, but relay 353 is slow in releasing and the release of relay 353 closes a circuit for operating relay 350'. This circuit is traced from battery through the winding of relay 35B, upper back contact of relay 353, inner upper back contact of relay 331, a front contact of relay 359, to ground at the lower back contact of relay 342. Relay 350 closes a circuit for holding relay 359, disconnects the windings of relays 357 and 358 from the conductors of dial jack DJ, opens the repeater termination consisting of resistor 3'1! and condenser 3'52 normally connected across conductors 373' and 314. The operation of relay 350 connects conductors 35I and 352 to talking condensers 335 and 336 and connects these conductors through the windings of retard coil 343, windings of relays 3M and 342, through resistor 343 to ground. The trunk circuit IDT is now in condition for talking between the intermediate operator and the answering subscriber, relays 354, 355, 355, 353 and 353 all being operated. With relay 3l5 operated due to the called subscriber having removed the receiver from the switchhook, the circuit through the lower winding of relay 3% is opened so as to increase the resistance in the circuit through conductor 333 to extinguish the supervisory lamp associated with the calling plug 0P4. If the called subscriber replaces the receiver, relay 520 releases, thereby causing the release of relay 315; and the release of relay 315 again closes the circuit through the lower winding of relay 354 to effect the lighting of the supervisory lamp associated with the calling plug CP4.

In order to complete a talking connection between the calling operator in the first toll office and the called subscriber, the intermediate toll operator must disconnect the answering plug from jack J4 and must also disconnect the calling plug from jack DJ. When the answering cord is disconnected from the jack J4 of the incoming trunk circuit, relays 424, 425 and 428 are released in succession thereby disconnecting ground from conductor 464 to effect the deenergization of the upper, operating Winding of relay 355 of trunk circuit IDT. When the calling plug SP3 is disconnected from dialing jack DJ, relays 354 and 355 release in succession. The release of relay 355 causes the release of relay 355 and causes the operation of relay 36'! in a circuit which includes the lowermost back contact of relay 355 and a front contact of relay 353. The operation of relay 361 causes the release of relay 350 and connects ground to conductor 333 to hold the selector CS and thus maintain the connection with the called line. The release of relay 355 causes the operation of relay 3'50, the circuit for operating relay 310 being traced through the upper back contact of relay 33B, upper back contact of relay 356, to ground at the inner upper front contact of relay 35$. The release of relay 350 causes the release of relay 359, but relay 310 looks through its lowermost front contact, inner lower and inner upper back contacts of relay 368,

uppermost front contact of relay 315, conductor 303, brush 293, front contact of relay 2%, conductor 283, to ground at a front contact of relay 2?! of two-way trunk circuit TWTZ. Relay 3'!!! disconnects the incoming conductors 30! and 332 from trunk circuit IT and connects these conductors, through conductors 39! and 332 and back contacts of relay 5m to the left windings of re peating coil RC5, thus completin the talking connection between the calling operators cord CD! and the called subscriber. With relay 315 operated, due to the answer of the called subscriber, and since the selector CS has selected a trunk in a level on which the normal post springs 542 are normal, ground at the inner upper back contact of relay 5! is connected through the upper front contact of relay 52 lower back contact of relay 505, back contact of springs 542, through conductor 395 and a front contact of relay 310 of trunk circuit IDT to the winding of relay 355. Relay 365 operates, connecting the winding of supervisory relay 353 through resistors 363 and 354 and both windings of retard coil see to conductors 39! and 332 in parallel with the winding of relay 52! of the selector CS. After disconnection of the cord CD4 from jacks J4 and DJ, a circuit is closed from ground at the upper back contact of relay 359, through the lower front contact of relay 315, conductor 384, brush 234, a front contact of relay 283, and through conductor 234 to the Winding of relay 219 of two- Way trunk circuit TWT2. Relay 219 operates, thereby connecting signaling battery through its front contact, back contacts of relays 2'33 and 240, retard coil 259, middle winding of relay 275 and upper winding of retard coil 255 to the upper conductor of toll line TL! to cause the operation of composite signaling relay Ild of signaling circuit CS5. Relay I closes a circuit including a front contact of relay I H] for operating relay E; and relay E35 opens the circuit through the lower, low-resistance winding of relay I64 to extinguish the supervisory lamp associated with plug CPI of cord CDI. The aforementioned operation of relay 370 also connects conductor 303 to conductor 393 but this is Without effect since relay 505 of selector CS is not operated. Switchhook supervision is repeated by relays 520, 315, 2l9, I10 and N35 to the calling operator.

If the calling operator in the first toll office operates the ringing key of the cord circuit to transmit a ringing signal or rering signal, relay M0 is momentarily released to cause the release of relay 210 of signaling circuit CS2 in the manner described in the aforementioned King et al. patents. The release of relay 2H] causes the momentary release of relay N5 of two-way trunk circuit TWTZ, the release of relay 333 of intermediate dialing trunk circuit IDT, and the release of relay 52! of selector CS. The release of relay 353 closes a circuit from ground at the upper back contact of relay 359, through a front contact of relay 313, back contact of relay 355, winding of relay 38!, to battery at a front contact of relay 355. Relay 38! looks under control of relay 382, independent of relay 335. When relay 365 reoperates at the end of the rering signal, a circuit is closed from ground at the upper back contact of relay 359, through a front contact of relay 310, front contact of relay 336, upper front contact of relay 38!, through the winding of relay 382 to battery. Relay 382 operates, thereby closing a circuit for operating relay 383 and causing the release of relay 33!. Relay 383 closes a circuit for operating relay 384. The release of relay 38! causes the successive release of relays 382, 333 and 384, each of these relays being slow in releasing. If at the time relay 382 releases, relay 315 is released clue to the receiver having been restored to normal at the called station, a circuit is closed from ground at the back contact of relay 382, through the back contact of relay 38!, front contact of relay 384 and lower back contact of relay 315 for operating relay 368. The operation of relay 368 causes the release of relay 3'85. The release of relay 3'!!! disconnects conductors 3G5 and 302 from conductors 501 and 552, causing the release of relay 52! of selector CS; and reconnects conductors 30! and 382 to conductors 4t! and 452 of incoming trunk circuit IT to reoperate relay M5 and thus light the answering lamp AL4 as hereinbefore described. lhe release of relay 330 also causes the release of relays 335 and 355; and when relay 384 releases, relay 358 releases. The intermediate dialing trunk circuit IDT is thus restored to normal and the rering signal will be answered by the intermediate operator and handled as on a new call. The release of relay 52! causes the release of relay thereby closing a circuit for operating release magnet 529 to restore selector CS to normal.

When the calling operator in the first toll oflice disconnects cord CD! from jack J l, relays I04, I35 and I43 are released, the release of relay I49 causing the release of signaling relay 210 of signaling circuit CS2. The release of relay 210 causes the successive release of relays 215 and 21! of two-way trunk circuit TWTZ, and also causes the release of relay 335 of trunk circuit IDT and the successive release of relays 52! and 522 of selector CS, if the connection is at that time extended through trunk circuit IDT to the selector CS; or, if the connection. is at that time extended to the incoming trunk circuit IT, the release of relay 27!! causes the release of relay M0. The release of relay 2i"! disconnects holding ground potential from conductor 233 thereby causing the return of selector TSZ to normal, in the manner described in the aforementioned King et al. patent, and causing the release of relay 315. The release of relay 522 of selector CS causes the release of relay 525 and the operation of release magnet 525 in series with the common relay 546 to cause the shaft and brushes of selector CS to be restored to normal. When the shaft reaches normal, springs 545 are restored to normal causing the release of release magnet 529. The aforementioned release of relay 522 also disconnects ground from brushes 533 and 534 causing the release of relays 532, 633 and 595. If, at the time the originating operator disconnects, the connection is extended to the incoming trunk circuit IT, the release of relay 4H] causes the momentary operation of relay M3; and, if the plug AP4 has not been disconnected from jack J4, the operation of relay 4l3 causes the operation of relay 454. Since relay 4!!! does not re operate, the connection of the low-resistance winding of relay 454 in parallel with the winding of relay 424 increases the current through conductor 423 to light the supervisory lamp associated with plug A1 4 as a disconnect signal. When the intermediate toll operator disconnects cord CD4 from jack J4, relays 424 and M4 release; and the release of relay 424 causes the successive release of relays 425 and 428.

Assume now that the level in which trunkhunting occurs is a level in which the terminals are. connected to intertoll trunks. The termi- 'nals' 535, representing such a level, are: connected to a two-way trunk circuit TWTS associated with an intertoll trunk or toll line TLS. The associated circuit TWTG, outgoing trunk circuit T5 and signaling circuit CS" are all similar to the corresponding circuits associated with toll line TLi. Upon selection of the level represented by terminals the normal post springs 54.! are not actuated but the normal post springs 54 2 are actuated, thereby closing a circuit for operatively energizing the upper winding of relay 553. When relay 523 releases at the end of the first train of impulses, it closes circuits including the middle contacts of the eleventh rotary step springs for energizing the lower, locking winding of relay 553 and for operatively energizing the winding of relay 5&5. Relay 5fi5 connects conductors 353i and 592 to contacts of relay 535, connects conductor 394 to brush 534, and connects ground directly to the middle contacts of springs 54! and 5&2. Trunk-hunting occurs in the manner hereinbefore described, relay 53% being operated when an unguarded set of terminals is found. The operation of relay 530 extends the connection from conductors 38-! and 592, through front contacts of relays 5G5 and 538 and brushes 53! and 532, to the line conductors 55! and 552 of the trunk circuit TWT5. Since relay 5535 is operated, the operation of relay 5% causes the release of relays 521 and 522 in succession. Holding ground'potential at the front contact of relay 2i! of two-way trunk circuit TWT2 is connected through brush 235 of selector T82, conductor3il3, front contact of relay tit, back contact of relay 5%, conductor 353, front contact of relay 5G5, and through conductor 5K! to the winding of relay 536. to hold relay 53E: operated; and ground is further connected through conductor 515, the inner lower front contact of relay 555 and brush 533 to conductor 553, to hold the intertoll trunk circuit TW'Ifi. The operation of relay 5353' also causes the release of relay sill. Since relay 522 is slow in releasing, a circuit is closed for operating relay 5l9, this circuit being traced from the winding of relay 5H3, through the inner upper front contact of relay lower back contact oithe eleventh rotary step springs 539, through the inner upper front contact of relay 539, to ground at a front contact of relay 522. Relay 5m locks with its winding in parallel with the winding of relay 555, through a front contact of relay in parallel with the lower, locking winding of relay 5 5-3, through the middle contact of springs 539, back contact of relay 523, conductor 5H middle upper front contact of relay 555, conductor 393, inner upper back contact of relay 5%, outer upper front contact ofrelay @l'l, to con.- ductor 353 and thence to. ground at a front con.- tact of relay ill of two-way trunk circuit TWT2. Relay 5% disconnects ground from the armature of relay 52E to prevent the operation of release magnet 529 when relay 522 releases. Relay 5!!) also connects conductors 3M and 592 through talking-metal contacts to brushes: 531 and 532, in parallel with front contacts of relay 5*255. With both or relays 595 and 5H! operated, the aforementioned release of relay 5Ell'is ineffective to cause the operation of relay 552. When the intermediate toll operator dials the succeeding digits of the called route and subscribers number, relay 35? repeats these impulses through'the simplex circuit which-includes resistors 35!- and 362, windings of retard coil 350, conductors 391 and. 392,. front. contacts of relays: 510" and 530, through brushes. 531 and 532; to the trunk circuit TW'IE toefiect.theatransmission of corresponding signals. over the toll line 'I'Lfi. Supervisory signals received over the toll line TLS are transmitted over conductor 654 to the selector CS through brush 534, a front contact of relay 5H5, conductor 39- 1 to relay 3T5, relay 315 being operatedin response to off-hook. signals and released responsive to on-hook signals. As long as the plug CP4 of. cord CD4 is connected tojack DJ, the operation of relay 3T5 effects the extinguishing of the supervisory lamp associated with plug CP4, this being efiected at the upper back contact of relay 3'l5 in thatground is there disconnected from the lower Winding of relay 354-; and the reoperation of relay 375 in response to an onhook signal effects the reconnection of ground to the lower winding of relay 354 to again light this supervisory lamp. When the intermediate toll operator disconnects cord CD4 from jacks J4 and DJ, relays 425, 425 and 423 of trunk circuit IT and relays 354', 355, 353, 357, 358, 359 and 350 of trunk circuit IDT are released and relay 3-10 is operated in the manner hereinbefore described. The operation of relay 3'50 completes the talking connection between the toll lines TL! and TLS by connecting conductors 3M and 352'to conductors 3%! and 392. The repeating coil RC5 is not included in this connection; and, since relay 5l2 is not operated, relay 520 is not used. Normal post springs 5 H being normal, relay 365 of trunk circuit IDT is operated in a circuit through conductor 395 and the normally closed contact of springs 5m to ground at a front contact of relay 565; and relay 355 connects the winding of relay 355 to conductors 30'! and 302 so that relay 366 is controlled by signaling relay 210. When the calling operator releases the connection, all of the circuits are restored to normal in the manner hereinbefore described.

Assume now that the selector CS selects a level, for instance, the level represented by terminals 555, in which the terminals are connected to intertoll. trunks which are similar to the intertoll trunks in the level. represented by terminals 536, except that no supervision is to be given by the intermediate toll operator. Upon selection of this level, both of the sets of normal post springs 541 and 542 are actuated to disconnect ground from. conductor 355 and thereby prevent the operationof relay 355 of the intermediate dialing trunk circuit IDT;. and, since relay 3&5 is not operated, relay 386 is not connected to conductors 38.! and 302. Answering supervisory signals are transmitted from-the seizedintertoll trunk through brush 534 and afront contact of relay 565 to relay 375 of the intermediate dialing trunk circuit IDT; relay 375 repeats the supervisory signals through conductor 304, to relay 219 of two-way trunk. circuit TWT2; and relay 219 repeats. these signals over toll line TLI to control the supervisory lamp of the calling operators cord CDI' in the-manner hereinbefore described. When the calling operator disconnects, the outgoing trunk circuit OTI is restored to normal, signaling relay 2'! releases, two-way trunk circuit TWT2 is restored to normal, and a disconnect signal is transmitted over the selected intertoll trunk. The release of relay 21'! of two-way'trunk circuit TWT2 causes the release of relay 29!) to restore selector TSZ to normal, the release of relay 370 to restore the intermediate dialing trunk IDT to normal, and the release of relays 505, 530 and 543 of selector CS to restore this selector to normal.

If, when the brushes of selector CS are being advanced in a selected level to hunt for an unguarded set of terminals, all trunks connected to this level are busy, the brushes are advanced to the eleventh rotary position thereby actuating springs 539 to cause the release of relays 585, 5111 and 543, if operated. Relay 53!] operates and relay 525 remains normal. The operation of relay 530 causes the release of relay 501. With relays 591 and 5111 normal, relay 512 is operated. With springs 539 actuated, the operation of relay 512 connects interrupter 548, through resistor 518, front contact of relay 521, lower right winding of repeating coil RC5, and through the lowermost front contact of relay 512, to the upper winding of relay 5211. The alternate operation and release of relay 5211, under the control of interrupter 548, causes like operations of relay 315 to flash the supervisory lamp of the intermediate toll operators cord. The intermediate toll op erator may thereupon converse with the calling operator in the first toll oifice. If there is another call awaiting completion through the intermediate toll office, the intermediate toll operator may disconnect the calling plug AP4 from jack DJ thereby releasing relays 354, 355, 351, 358 and 359. Relay 35!) operates when relay 358 releases and relay 351 operates when relay 355 releases. The operation of relay 351 causes the release of relay 355. The release of relay 351 opens the simplex circuit through conductors 391 and 392 causing the release of relays 521 and 522 of se lector CS; and the selector CS is thereby restored to normal. The other call may now be completed either manually or through selector CS in the manner hereinbefore described. If the intermediate toll operator disconnects both the calling plug from jack DJ and also disconnects the answering plug from jack J4, relay 310 of trunk circuit IDT is operated in the manner hereinbefore described to connect conductors 3111, 332 and 393 to conductors 391, 392 and 393 and the alternate operation and release of relay 31.5 under the control of interrupter 548 now causes like operations of relay 219 of two-way trunk circuit TWT2; whereby an intermittent signal is transmitted over toll line TLI to cause corresponding operations of relays 110 and 105 to flash the supervisory lamp associated with plug CPI of cord CD1. When the calling operator disconnects cord CD1 from jack J 1, the trunk circuits and. selectors are restored to normal as hereinbefore described,

Calls completed through selector TS? Assume now that the intertoll dialing trunk circuit IDT is associated with the selector circuit TS1 shown in Fig. 7 instead of the combined in: tertoll and toll transmission selector CS shown in Fig. 5. In this case, when the answering operator inserts the calling plug CP4 in dial jack DJ of trunk circuit IDT, the operations of relays 351, 358 and 359 close a circuit for operating relay 111 of selector TS1. This circuit is traced from ground at the inner lower front contact of relay 359, through the lower back contact of rela 331, front contact of relay 351, back contact of test jack TJ 1, back contact of relay 353, middle lower back contact of relay 353, thence in simplex through resistors 361 and 352, front contact of relay 359, windings of retard coil 385, conductors 331and 392, back contacts of relay 116 of selector TS1, through resistors 101, 138 and 139 and the winding of relay 11 1 to battery. Relay 111 closes a circuit for operating the slow-to-release relay 112. Rela 112 connects ground through a back contact of relay 116 to the alarm circuit 199 to initiate an alarm operation in case no directive impulses are received within a predetermined interval of time. Relay 112 also connect ground to conductor 333, this being without effect since conductor 393 is connected through a back contact of relay 358 and a front contact of relay 355 to conductor 393, and thence through brush 293 of selector T82 and a front contact of rela 295 to ground at a front contact of relay 2110f twoway trunk circuit TWTZ. .When the intermediate toll operatordials the first digit of the called toll route number, each release and reoperation of relay 351 causes a like release and reoperation of relay 11 1. The release of relay 11 1, in'response to the first dial impulse, closes a circuit from ground at the back contact of relay 116, through the back contact of relay111, a front contact of relay 112, Winding of relay 113 and through the winding .of vertical stepping magnet 1!1 to battery. .Relay113 and stepping magnet 111 are thereby. operated, theoperation 0f magnetlil being efiective to step the brushes of selector TS1 up to the first level of the terminal bank. The release of relay 111, at the end of the first impulse, causes the release of vertical stepping magnet .111; but relay 113 is sloW-to-release and remains. operated until all ofthe impulses in the train have been received by relay11 1. Relay 192 is also slow-to-release andit remains operated While relay 111 is. responding to dial impulses. The vertical off-normal springs 121 are actuated as soon as the shaft on which the brushes are mounted moves out of normal position, thereby closing a circuit from battery through thewinding of relay 115, upper contact of vertical offnormal springs 121, front contact of relay 113, to ground at a front contact of release relay 152. The release and reoperation ,ofrelay H1 in response to each succeedingimpulse of the train effects a corresponding operation and release of the vertical stepping magnet 111 thereby advancing the brushes of switch TS1 to the level corresponding to the digit dialed. When relay 1E3 releases at the end of the train of impulses it opens the operating circuit of relay 1'1 5; but relay 115 is held operated under control of springs 12! and the back contact of rotary stepping magnet 118. The release of relay 113 closes a circuit for operating the rotary stepping magnet 113, this circuit being traced through the upper front contact of relay 115 and the upper back contact of relay 113, to ground at the uppermost front contact of relay 112. The operation of stepping magnet 118 advances the brushes of switch TS1 into engagement with the first set of terminals in the selected level. The operation of stepping magnet H8 also causes the release of relay 115; and the release of relay 115 causes the release of stepping magnet 118, When stepping magnet 118 releases, it closes a circuit from battery through the Wind ing of relay 115, through the upper front contact of vertical off-normal springs 121, back contact of stepping magnet 113, middle lower back contact of relay 116, through test brush 133 to the test terminal engaged-thereby. If the selector or trunk circuit connected to the engaged set of terminals is busy, brush 133 encounters a busy ground. potential which causes the reoperation of relay 115. The reoperation of relay 115 causes the reoperation of stepping magnet 118 to advance the brushes of selectors TS! into engagement with the next set of terminals in the selected level. If the test terminal of this next set of terminals is also connected to ground, relay H5 is again operated to continue the advance of the brushes of selector TSI. When the brushes engage a set of terminals connected to an idle trunk or selector, relay H5 does not reoperate since the terminal engaged by brush I33 is free of ground potential; and relay H6 is operated by the current in a circuit traced from battery through the winding of relay H5, upper contact of vertical off-normal springs 12!, back contact of rotary stepping magnet H8, winding of relay IIIi, lower contact of the eleventh rotary step springs I22, to ground at the uppermost front contact of relay I I2. Relay I I5 is marginal and does not reoperate in series with the winding of relay H6. Relay IIG disconnects the winding of relay II! from conductors I! and I02 and connects these conductors to and through brushes I3! and I32, to the talking conductors of the trunk connected to the engaged set of terminals. Relay IIB connects the grounded conductor 393, through brush I33, to the test conductor of the selected trunk circuit to mark this trunk circuit busy and thereby guard against its selection by another selector having access thereto. The release of relay H I, when its winding is disconnected from conductors 39! and 392, causes the release of relay H2. Relay IIZ disconnects ground from conductor 393 but relay I! 6 is held operated, since conductor 393 is connected to ground at a front contact of relay 21! of two-way trunk circuit TWTZ as hereinbefore described.

Assume now that the selector TS! has selected the level represented by terminals I42, the terminals in this level being connected to trunks to a community dial oflice; and assume that the trunk circuit CDTI, which is connected to terminals I42, is the first idle trunk circuit in the group. When relay H6 operates, a circuit is closed for operatively energizing the line relays 8I0 and 8| I of trunk circuit CDT! is traced from ground at a front contact of relay 359, back contact of relay 351, front contact of relay 351, conductor 349, back contact of relay 344, back contact of relay 368, thence in simplex through resistors 35! and 362, front contacts of relay 359, windings of retard coil 300, conductors 39! and 392, front contacts of relay H3, brushes I3! and I32 of selector TS'I, through conductors 80! and 802 of trunk circuit CDT! both windings of retard coil 800, thence through conductor 809, winding of relay BIO and a winding of relay 8! I to battery. Since the trunk circuit CDT! is associated with a trunk CDT to a community dial office in which it is necessary to connect the trunk circuit to an idle selector before the calling operator dials the next digit of the called subscribers number, the left-hand normal pest springs I25 of selector T! are actuated upon selection of the level in which the terminals I42 are located to connect ground to conductor 394 as a stop dial signal. This connection is traced from ground at a front contact of relay II 2, through the front contact of normal post springs I25, lower back contact of relay 'II3, upper back contact of the eleventh rotary step springs I22, through conductor 394, to the winding of relay 315 of intermediate trunk circuit IDT. Relay 315 is thereby operated, connecting ground directly to conductor 349, independent of any further operations of relay 351, to prevent the transmission of further This circuit windings of relay 820.

impulses over the simplex circuit through condoctors 39! and 392, until the selector in the community dial oflice is ready to receive impulses. The operation of relay 315 disconnects ground from the lower Winding of relay 354 thereby increasing the resistance in the circuit through conductor 353 to cause the lighting of the dial pilot lamp at the intermediate dialing operators position. After relay H2 releases, due to the operation of relay 5 i 6, conductor 335 is connected through the upper back contact of springs 722, a front contact of relay lit, through brush 134, to conductor 803 of trunk circuit CDTI, thence through a back contact of relay 32! to ground at the back contact of relay tit. The aforementioned operation of relay 9H1 closes circuits for operating relays 8I2, 9M and M5. Relay 8I2 closes a circuit for lighting the busy lamp, such as 3L3 associated with outgoing jacks to which trunk circuit CDT! is connected, and connects battery through resistor 9 i l and the upper winding of relay 930 to the sleeve of the associated jacks at the toll board to mark the trunk CDT! busy. Relay 8I4 locks through its upper winding, conductor 803, brush I33 of selector T51, a front contact of relay H3, conductor 353, a back contact of relay 368, a front contact of relay 359, to conductor 333 and thence to ground at the front contact of relay 2?! of two-way trunk circuit TWTZ. Relay 3H! disconnects ground from the lower winding of relay 833 to prevent operation of relay 336 if an operator should disregard the busy indication and plug into a jack to which trunk circuit CDT! is connected. Relay 8I4 also disconnects the winding of relay 83! from conductor BIS so as to prevent the false operation of relay 93! and relay 8i4 short circuits the upper winding of relay 820 thereby causing the operation of the marginal line relay I00! of trunk circuit CDTZ in the community dial oflice at the distant end of the trunk CDT. relay 8I5 locks through its upper winding to grounded sleeve conductor i303 and disconnects this conductor from the contacts of relays 8I2, 33! and 833. The lower contacts of relay 8I5 facilitate testing of this relay.

While the trunk CDT between the toll office and. the community dial oflice is idle there is a closed circuit through the winding of line relay I00! of trunk circuit CDTZ in the community dial office, in series with the left windings of repeating coil RCIfl, conductors 85! and 852 of trunk CDT, right windings of repeating coil RC8 of trunk circuit CDT! in the toll oflice and both Relay 820 is polarized and does not operate since the current in this normally closed circuit is in the non-operating direction. Relay I09! is marginal and does not operate since the upper winding of relay 820 has a high resistance. When the upper winding of relay B20 is short-circuited by the above-mentioned operation of relay 8 I4, the current through trunk conductors 85! and 832 is increased sufficiently to cause the operation of relay I00! in the community dial office. Relay I00! closes a circuit for operating the slow-to-release relay Relay I032 closes a circuit for operating relay I003, connects ground to conductor I043 to mark trunk circuit CDT2 as busy in the banks of selectors SI having access thereto, connects the winding of relay I099 to conductor I033 to mark the terminals of trunk CDT2 in the banks of trunk finder TF having access thereto, and closes a circuit for operating group relay IBIO. With relays I00! and I093 operated, the winding of 

